1. Field of the Invention
The present invention relates to a dielectric ceramic composition and a laminated ceramic capacitor using the same, especially to a ceramic capacitor having inner electrodes made of Ni.
2. Description of the Related Art
Ceramic layers and inner electrode metal layers are alternately stacked in the laminated ceramic capacitor. A cheap base metal such as Ni has been recently used for the inner electrodes in place of expensive noble metals such as Ag and Pd for reducing the production cost. When Ni is used for the electrodes, the capacitor should be fired in a reducing atmosphere where Ni is not oxidized. However, ceramics comprising barium titanate as a principal component may be endowed with semiconductive properties when the ceramics are fired in a reducing atmosphere. Accordingly, as disclosed for example in Japanese Examined Patent Publication No. 57-42588, a dielectric material in which the ratio between the barium site and titanium site in the barium titanate solid solution is adjusted to be larger than the stoichiometric ratio has been developed. This allows the laminated ceramic capacitor using Ni as electrodes to be practically used, thereby expanding its production scale.
Since electronic parts have been rapidly miniaturized with the recent advance of electronics, small size ceramic capacitors with large capacitance as well as temperature stability of electrostatic capacitance are required. The ceramic capacitors having the Ni electrodes are also under the same circumstances.
For complying with the requirements of large capacitance and small size, the dielectric ceramics should be made to be thinner and multi-layered. However, much higher voltage is impressed on the dielectric material when the dielectric ceramic layer is thinned, often causing troubles such as decrease of dielectric constant, increase of temperature dependency of the electrostatic capacitance and deteriorated stability of other characteristics when conventional dielectric materials are used. Especially, when the thickness of the dielectric layer is reduced to 5 .mu.m or less, 10 or less ceramic particles are contained between the inner electrodes, making it difficult to assure a stable quality.
Making the dielectric layer thin is accompanied by other problems. Solder plating layers as external electrodes are usually formed on the baked electrodes of a conductive metal powder in order to comply with automatic packaging of the laminated ceramic capacitor. Therefore, the plating layer is generally formed by electroplating. Oxides containing boron or a glass is added, on the other hand, into some dielectric ceramics as a sintering aid. However, the dielectric ceramic using these additives has so poor resistance against plating that characteristics of the laminated ceramic capacitor may be deteriorated by dipping it into a plating solution. It has been a problem that reliability is markedly decreased in the ceramic capacitor having thin dielectric ceramic layers.